Poly-alpha-olefins stabilized with long chain alkyl gallates



- Uni ed .i e k s Peefltq; 1

"PO Ya-Q EE STAB LI D 40 5 97 i CHAIN AEKi9aLFeT.E.- t V .t Clarence E.Tholstrup and Alan Bell, Kingsport, Tenn., assignors to EastmanKodak;Company, Rochester, wflfuwme a n q Ne J rs No Drawing. ApplicationOctober 18,.1957 I -'SerialN0."690,'890

Claims. (Cl. 260-4535) ll his invention relates tot-he stabilizationof-organic .s po dswh szh are subiecttoflogtid d radatigni through theinclusion of certa" 0f ganic 391d MQilliQii flcarbon atoms, in organicplasticcornpos polymerized toirfrlqli'dolffiiisi ilf -oxidants withfats, oils, a r d-..;fat ff U hen used alone orin synergistic ca ac.able preference has been'shownyhow Another'object of the presentinvention is to provide such compositions of matter comprising'poly-u-mono- P idi kifiiiFffl}? olefins in combination yvith certainlong chain alkyl esters- $3, 3 i P? h i i qii of gallic acid wherein the-a1k'y1 group contains 12-18 would not enhance the antioxidant ch ascarbon atoms 'galli c riioiety due to "stericefiects'f""M'orepv v-tEtiiti'oxidaiit potency' per ufiitfof iiioleculafvve ght'vvo ldie bexpected for the highei alky'l g'a'natesfi Alsa, 15 or 'alkyl" gallatessuch as'etliyl ofpropy V used to stabilize polyrn'eri'c' coin 'jositionss'ulzhas ethylene. It would be an obvious ixpectatio" when tested onan'equal Weight basis, the pjoren I gallate compounds would tend todecrease asithe ester group incr eas es'to fairly larg e sizeandvveight. Thus, it would be" supposedfthat 'as the 'alkyl moietybeco'r'ne's larger; the active antioxidant gallic 'inoiety vvouldbeconie smaller in pr0'portion, resulting 'in'a cominensur e decrease inthe relative antioxidantfcapabilitygot thecompound. For example, inthe"propylfgallate molecule, the "active 'gallic moiet conipris'es'aboutj'8 0 %"of fthe'figvei ght of the, molecule; whereasgin dodecyhg'allate thefjacfiye gallic'irioiety.comprisefonly aboutl'%fof t hernol'L 10mg" chain 'a lkyl' gallate's, such ;as la'uryl g allat beenjsuggest'ed 'as antioiidants for foodsfco 'con'su'tuentsj whereby thereisacli' a compatibility even though the-presenc V V I s'ixnilar' largeallcyl radical obviously dir'nini 1 es the p 'o- 'port ion of 'theactive gallic rnoityin inversekelajtion to the size of such alkylradicals. As 'to thef "compatibility {of propyl gallatein organicplastics siich"as polyethylene,

aforementioned compositions wherein the gallic ester stabilizers possessthe properties of unusually low volatility,

9 d uhereinth t Still another object of this invention is to provide thehese ompost.

itiiszpointed out in prior art such as BritishPat'entNo. ;O53:* "'Sv19,57 nqwmatentor --618,839'that a Wide range of proportions" can be'enflployed such as 0.05% to'5% by weighttl'thusjenhancedicornpatibility over pr opyl g'allate isobviously iiot'l't edlii'red.=Moreover,-buty1 gallateand it s'branchedchain on efrs normally havesubstantially no 'be'tter laiitioitidant prop- -erties thanthe adjacent-propyl fho r'nolofgj iltfl't herefore appears that'there'wo'uld benothing to' gain an rnuch I to be lost in trying higher alkylihornologs. fl 'uitherinp fi the parent compound, gallic aciditselfi ha's shownhighly satisfactory results in the other direction,li.e., tw the 5-"an'tioiiitlantcapability of propyl gallate.

8;' Y Bl el -e des ribe d tai his testingjP M e a i I t 1 S abilitw h np y i y testedat C; ratherrthan erat k for polyethylene. EXia'eri- Vakesv itclear that polyethylene isiibt a I a en of polymerizedhomolqgs7such'jas:pr3- ene to. since poiyethylenehasamuchhiglier rentstability. ".More over theothe'r poly-ia-morioole- Withyvh iiithislinvention isparticularlyconcernedare or 'sydiotactic polymers.

' te that a particularly outstanding With these considerationsin mind,it is apparent that it eefinii tigiin nes in the unexpectedly'achievedto those skilled in the" an i the present invention qu te :i'i' envious.'Thus, it has no'w been found th v along =chain alkyl esters of gallicaeid, jn'ore arly ithe "alkyl esterswherein the ""ilk yl g rouficontains' 1'2"-1'8" greater thermal; electrical,and pxidativestabilityxiffhus,

1i s l m ts re is adamage fromwhaas h rtigs, ygother especiallyrivaluabie itstabilized polymers relates to their exceptional resistanceto degradation during extrusion or while otherwise shaping polymers athigh temperatures.

Moreover, this invention provides stabilized compositions in whichinclusion of the stabilizer doesmot impart a stain or discoloration tothe product. I This advantage is especially worthwhile when it isdesired to ncorporate a pigment. Moreover, inasmuch as the stabilizersas advantageously employed according to this inventlon do not causediscoloring of the product, the stabilized synthetic resin maybe-colored in more delicate shades than'when a stabilizer causingdiscoloration is used in amounts required for effective stabilization.Thus, the product is better adaptable for use in the manufacture ofcontainers and wrappers for food and the like. Along with improvednon-staining characteristics, the specified longchain alkyl esters ofgallic acid are highly compatible with poly-a-olefins, making themeasily introduced into an organic plastic composition. Moreover, theesters of our invention display excellent low volatility which isanimportant advantage, especially in products which are subjected toelevated temperatures or other conditions where the stabilizer may bepartially lost. The poly-a-monoolefins referred .to'in thi inventioninclude polyethylene, polypropylene, polybutene-l, and their copolymersas well as other polymerized u-monoolefins such as 2,2-dimethylbutene-1.

The high molecular weight esters of gallic acid within the purview ofthe invention are represented by the following general structure:

O HO lib-O-R any desired modifiers or pigments, on heated rollsinaccordance with conventional practice. The composition can be removedfrom the rolls thereafter. If desired, 'it can be comminuted by means ofa cutter such as a Roll and Jewel cutter. Other means of preparing thestabilized compositions can also be employed, such as mixing in aBanbury mixer or other standard mixing equipment. If desired, the estercan be incorporated --with the poly-u olefin in a solvent which can beremoved by subsequent working and seasoning.

The compositions of this invention can include modifiers, plasticizers,lubricants, coloring matter, fillers, or other synthetic or naturalresins, in addition to combinations of other stabilizers, antioxidants,and metal deactivators known for retarding the catalytic eliect of iron,copper or the like in promoting oxidation. Either colored or colorlessproducts may be produced employing a suitable choice of such materials.

The compositions of this invention can be extruded or molded accordingto conventional techniques to furnish finished articles in the form ofsheets, rods, tubes, films, filaments, nuggets, or any other physicalshapes commonly assumed by polyolefinic compositions. An efiicaciousantloxidant is particularly important during the extrusion ofpoly-a-monoolefins, such as during film manufacture, for without one,small portions of the polyolefin which remain at the head of theextruder for lengthy periods of time at elevated temperatures decomposemto solid obstructions thereby requiring frequent shutdowns to permitcleaning of the. ext uder.

Taea'saoo p r The invention and its unobviousnessis further illustratedbut not restricted by the following tables wherein examples showpoly-a-monoolefins stabilized with gallic acid and gallic acid esters,These tables clearly show the remarkable results obtained when the alkylesters have 12-l8 carbon atoms in the alkyl radical. The aforementionedthermal stability test was used to .obtain the results shown; thepercentages of the stabilizer compounds are based on the total weight.

' TABLE I Oven life of polyethylene +0.10% stabilizer measured at C. bydescribed thermal stability test Stability As Hours of Oven LifeStabilizer 1. None (Control) 2. Short Chain Alkyl Gallates:

(b) propyl ester (c) butyl ester (d) isobutyl From Table I it isapparent that the miscellaneous esters (alkyl and aryl) encompassedwithin items 2 and 3 are no better than gallic acid. Moreover, there isnot any significant variation of properties among the various alkylgallates which would indicate that propyl gallate (which has provencommercial adequacy) could be greatly improved upon. Thus, it wouldappear from items 2, 3 and 4 of this table that in general all esters ofgallic acid are substantially equivalent in degree of efficacy. It wastherefore quite surprising to find, as clearly demonstrated by item 5 ofTable I, that a limited number of long chain alkyl esters possess anentirely different order of stabilizing potency. This represents aremarkable difierencein kind in the results achieved.

The results shown in item 5 of Table I are representative of similarresults which can be achieved using the '13, 14, 15, 16 and 17 carbonatom homologs as well as the isomers of the 12 and 18 carbon atom alkylgallates shown in item 5.' Such homologs and isomers include tridecylgallate, tetradecyl gallate, 2-ethy1tetradecyl gallate, pentadecylgallate, hexadecyl gallate, S-methyl-hexadecyl gallate, heptadecylgallate, etc.

When. the testprocedures employed in gathering the results for Table Iwere repeated using 10 times as much of some of the stabilizers, it wasfound that the ratios of oven lives for stabilized polyethylene to thecontrol sample were no more than about doubled for propyl gallate,cyclohexyl gallate and gallic acid (none others except dodecyl gallatewere tested). In contrast, when 10 times as much dodecyl gallate wasused, the achieved oven life ratio remained substantially the same. Thisdemonstrates another unexpected feature of this invention in that thelong chain alkyl gallates of the invention can achieve their excellentresults at unusually low concentrations whereas a previously knowngallate such as propyl gallate even at 1.0% concentration is but littlemore effective than at 0.1% concentration.

Table II shows the stabilization of isotactic polymers or a-monoolefinswhich is similar to the results achieved in regard to stabilizingpolyethylene as shown in Table 1. Similar results can be achieved asregards other isotactic and .syndiotactic polymers such as can bederived from 3'm6thylbi1 t1 1?1 pentene-l, 3,3-dimethylbutene-1, "4

methylpentene-l, 4,4-dimethylpentene-1 and other amonoolefins containingfrom 3 to 8 carbon atoms such as styrene and includes the variouscopolymers.

TABLE II Oven life of polypropylene +05% stabilizer measured at 140 C.by described thermal stability test Stability Stabilizer As Hours ofOven Life 1. None (Control) 0.5 2. Pro yl Gallat 7.0 3. Do ecyl (innate70.0

of a-monoolefins containing from 3 to 8 carbon atoms 3. Substantiallyisotactic polypropylene in, an essen- 'tially solid. state stabilizedwith an alkyl ester of gallic acid wherein the alkyl group contains12--.18 carbon.

atoms. l

4. Polyethylene in an essentially solid state stabilized withabout 0.10%by weight, based on totalweight of In addition to the compositions ofmatter covered by 7 this invention, it also covers the related processessuch as a process for stabilizing a solid colorless polyu-monoolefinagainst oxidative degradation whereby about 0.001% to 3% by weight of analkyl ester of gaIlic acid wherein the alkyl group contains 12-18.carbon atoms is combined at above 140 C. with said poly-asmonoolefinwithout appreciable staining of said composition, whereby a stabilizedsolid poly-a-monoolefin is formed characterized by being substantiallycolorless, retaining its electrical ro erties durin ex osure to elevatedtemperatures v l r p p g with about 0.05% to 3.0% by we ght of thedodecyl ester p of gallic acid.

for extended periods of time, and being 'free from loss due tovolatilization or separation ofsaid stabilizer at elevated temperatures.

This invention produces especially efficacious. and un I obvious resultsat stabilizer concentrations of from 0.01% to 0.05% by weight inpolyethylene and from 0.05% to 3% by weight in the otherpoly-u-monoolefins such as polypropylene, etc. Of course, higherquantities can be used in both cases, but generally there is relativelylittle additional advantage to be'gained thereby. A very valuableattribute, of the stabilizers of this invention in polyethylene is thatthey serve quite effectively at concentrations such as 0.05% by weight;whereas, even 1.0% of propyl gallate only improves the AOM stability bya factor on the order of 2m 4 times and concentrations as low as 0.05%are practically ineffective. In contrast, the small amount of 0.1% ofdodecyl gallate results in an improvement factor on the order of morethan 30 times (see Table I) and less than half this concentration (lowerthan 0.05%) is still highly effective. In fact, it is generally quitefeasible to employ 0.05% by weight of the stabilizers of this inventionas an effective concentration in polyethylene of standard commercialquality.

Although the invention hasbeen described in consid-' erable detail withreference to certain preferred embodimodifications can be effectedwithout departing from the r spirit and scope of the invention asdescribed hereinabove compositiomof an alkyl ester of gallic acidwherein the alkyl group contains 12-l8 ,carbon atoms.

, '5. Polypropylene in an essentially-solid state stabilized 7 withabout0.5% by weight, based on total wcightgof composition, of-analkyl esterof gallic acid wherein the alkyl group contains l 2-18 carbon-atoms.

6. Polyethylene in an essentially solid state stabilized with about0.001% to 0.05 by weight of the octadecyl ester of gallic acid. I l

7. Polyethylene in an essentially solid state stabilized ester of gallicacid.

8. Polypropylene in an essentially solid state stabilized with about0.001% to 0.05% weight of the dodecyl 9 Polypropylene in an essentiallysolid statestabilized "with about.0.05% to 3.0% by weight of theoctadecyl ester of gallic acid.

10. A process for stabilizing a solid colorless poly-amonoolefin againstoxidative degradation whereby about 0.001% to 3% by. weight, of an alkylester of gallic acid wherein the alkyl group contains 12-18 carbon atomsis combined at above C. with said poly-u-monoolefin without appreciablestaining of said composition, whereby a stabilized solidpoly-a-monoolefin is formed characterized by being substantiallycolorless, retaining its elec- References Cited in thefile of thispatent UNITED STATES PATENTS 2,448,799 Happoldt Sept. 7, 1948 I FOREIGNPATENTS a V 618,839 Great Britain Feb. 28, 1949 Bergelz' Chemistry andIndustry, Apr. 1, 1944. pages 1 127-128. (Copy in Scientific Library.)

1. A SOLID POLYMER OF AN A-MONOOLEFIN SELECTED FROM THE GROUP CONSISTINGOF POLYETHYLENE, SUBSTANTIALLY ISOTACTIC POLYMERS OF A-MONOOLEFINSCONTAINING FROM 3 TO 8 CARBON ATOMS AND SUBSTANTIALLY SYNDIOTACTICPOLYMERS OF A-MONOOLEFINS CONTAINING FROM 3 TO 8 CARBON ATOMS STABILIZEDWITH ABOUT 0.001% TO 3% BY WEIGHT, BASED ON TOTAL WEIGHT OF COMPOSITION,OF AN ALKYL ESTER OF GALLIC ACD WHEREIN THE ALKYL GROUP CONTAINS 12-18CARBON ATOMS.